Process of making wood pulp



PATENT OFFICE.

EDWARD F. MILLARD, OF HOPKINTON, MASSACHUSETTS.

PROCESS OF MAKING- WOOD PULP.

No Drawing.

T 0 all whom it may concern:

Be it known that I, EDWARD F. MILLARD, citizen of the United States, residing at Hopkinton,in the county of Middlesex and State of Massachusetts, have invented certain new and useful Improvements in Processes of Making Wood Pulp, of which the following is a specification, reference being had therein to the accompanying drawmg.

My present invention relates to an improved process of making wood pulp, and has for its principal object the reduction of pressure to the wood stock and the elimination of the use of hard grindstones.

In making wood pulp it has previously been the custom to place the wood stock'in a cylinder or other suitable receptacle and subject it to a high pressure whereby it is forced against a grinding stone which is rotated to remove the fibre, the grindstones used being of hard material to withstand the pressure. Only hard grindstones have been employed and the pressure has been adapted to the condition of the stone whether sharp or worn and smooth, and a relatively light pressure has been employed in connection with a sharp stone. Such grindstones when first dressed produce a large proportion of slivers and short thick particles, which weakens the pulp. As the stone wears smooth, a better pulp is produced, but a,

large quantity of wood flour is made, which goes to waste, also cutting down the production.

In carrying out my present process I propose to place the wood stock in the usual form of machine, such as illustrated in my Patent No. 780,213, dated January 17, 1905,.

having a cylinder or other form of receptacle therefor, but instead of using high pressure to force the stock against the grindstone, I will use the minimum amount of ressure necessary to cause the stock to rictionally engage the grindstone which will be of relatively soft material such as sandstone, or manufactured stone having a soft bond. I refer to the minimum pressure Specification of Letters Patent.

Application filed June 7,

Patented Apr. 18, 1922. 192i. Serial No. 475,775.

explained in the aforesaid patent, namely a relatively light pressure, that is to say approximately 3500 lbs., which is approximately one-third of what is commonly used in heavy pressure machines. By a soft grindstone I mean a grindstone in'which the grit is held loosely adherent by a soft bond. A stone of this character will not take a polish or wear smooth, has a surface of the desired roughness (the nature and quality of the surface not being affected as the elements wear),-and produces fine and long fibres which are uniform. The stone will give oft particles on its active periphery to maintain the substantially constant and uniform frictional engagement between the stone and wood stock, thus eliminating excessive pressure as well as minimizing drive power. For making short fibres a fine grit stone is necessary, whereas to produce long fibres a coarse grit stone is preferable. It is hardly possible to get these natural sandstones of both fine and coarse grit, and for this reason it is necessary to dress the stone to get both fine and coarse grit results. On the other hand, if desired, manufactured stone having a .soft bond may be used.

Having described my invention, what I claim as new and desire to secure by Letters Patent, is:

The method of producing uniform mechanical fibre from raw wood without flour or coarse particles, which consists in presenting wood to *a grinding surface of grit and soft bond such that it would be substantially efi'acedunder the usual grinding pressure and applying to such wood-and grinding surface a pressure so light that it would not substantially efi'ace said soft grinding surface.

In testimony whereof I hereunto aflix my signature in the presence of two witnesses.

EDWARD F. MILLARD.

Witnesses:

ERNEST H. ADAMS, ALBERT B. C. DEMING, Jr. 

